[blucar]

Looking at the grille shown in your photos, the truck is a '66.. The '65 grille had square opening similar to the earlier '64.
The engine appears to be a stock original 352 FE series engine... This engine can be replaced with any FE series engine, 360, 390, 428.. All of which are big block engines...
The FE engine where generally lumbering giants, slow turning fuel gulping monster... They had very soft valve guides/valves, requiring a valve job at about 60k and a total rebuild at 90k..If the trans is a 4spd it will be a T18 New Process. If you pull the engine keep the front mount, you will need it if you want to put another FE series engine in the truck..
If you intend to repair/rebuild the truck forget the engine.. very costly and not friendly with today's fuels.
A good choice of engines would be a late model 351 Windsor.. The Windsor engine will bolt up to the T18 trans using the bell housing from a 240/300 CID 6 cyln.
A second good idea would be to find a style side bed... Step side beds are only in favor with a small hand full of pickup truck owner's..
Trucks are enjoying a very large following, they are cost effective to build and they can be used for many daily jobs...
I have a '66 F-250 4 x 4 with a '68 390 engine... I am currently parting out a '66 F-250 & a '64 F-250..